Generally, a cylinder is determined based on an output signal from a crank angle sensor and a cam angle sensor and a crank angle is detected to perform an ignition control or fuel injection control when the engine is being operated. Therefore, the first firing and injecting cylinder is unclear until the engine is cranked by a starter to complete the determination of the cylinder. Accordingly, upon the start of the engine, the fuel injection is performed to a cylinder that can combust the fuel as fast as possible and ignition is performed to generate a first explosion to start the engine, after the cylinder determination is completed.
However, in this starting method, a cranking period to some degree is required by the completion of the cylinder determination and fuel is injected to the first cylinder performing the intake stroke after the completion of the cylinder determination. Therefore, taking a four-cylinder engine as an example, two to three strokes are required from the start of the cranking to the first explosion, thereby entailing a disadvantage that the starting time increases by that much. When the starting time increases in a vehicle having mounted thereto an idle stop system wherein the engine is automatically stopped (idle stop) when a predetermined automatic stop condition is established during the idling and the engine is automatically restarted by an operation on an accelerator pedal by a driver, in particular, the driver is likely to feel slowness upon the restart or the driving sound of the starter becomes a jarring noise, so that the demand for shortening the starting time is strong.
Japanese patent document JP-1-170735A discloses a method of performing an injection asynchronous with the starter wherein fuel is injected to all cylinders in synchronicity with the starter signal. The fuel is sucked into the cylinder performing the intake stroke at this time and ignition is performed via the compression stroke to generate the first explosion in order to shorten the starting time.
Alternately, Japanese patent document JP-11-107823A discloses a method wherein an engine stopping position is estimated and stored in a memory when the engine is stopped and a cylinder that is to be firstly fuel-injected and fired is estimated based on the stored engine stopping position during the next engine starting operation.
However, both starting methods described above require a process in which fuel is injected and sucked into the cylinder performing the intake stroke after the start of the cranking. Then, ignition is performed during the compression stroke of the cylinder. Therefore, a period of almost two strokes is required from the start of the cranking to the first explosion, with the result that the required starting time cannot be satisfied in the case of restarting after the idle stop. Additionally, in the injection system asynchronous disclosed in Japanese patent document JP-1-170735A, fuel is injected to all cylinders at the beginning of the starting operation so that the fuel not used for the combustion is emitted intact, thereby entailing a problem of deteriorating the exhaust emission during the starting operation.